The present invention generally relates to automobile antenna systems, and, more particularly, to a method and system of providing three additional dimensions of freedom to an in-glass antenna that facilitates impedance matching of the in-glass antenna.
Automobile FM radio receivers typically use monopole antenna structures, such as mast or telescoping whip antennas, to provide an acceptable level of reception of radio signals in a moving motor vehicle. The downfall with these antennas is that the extension of these antennas from the body of the motor vehicle exposes the antenna to damage or contact with debris during travel. In addition, these types of antenna designs detract from the overall appearance of the motor vehicle, induce wind noise and often include expensive systems that are used to retract the antenna into the body of the motor vehicle when not in use to protect the antenna from damage.
Concealed or conformal antennas, such as those embedded in windows of motor vehicles, have been used to overcome these problems. U.S. Pat. No. 5,610,618, to Adrian et al., discloses an automobile antenna system that uses a conductive trace that is placed within a portion of the glass of an automobile window lite. As set forth in greater detail below, the present invention may be used in an antenna system like that disclosed in U.S. Pat. No. 5,610,618 and, as such, this patent is hereby incorporated by reference in its entirety for background purposes only.
Concealed antennas are difficult to design to meet the same level of quality of conventional monopole aerial antennas. One reason for this is because impedance matching concealed antennas with the radio receiver of the motor vehicle can be difficult. The performance of an antenna is in large part determined by its impedance match with the radio receiver. In designing antennas for use in motor vehicles, it is important to match the impedance of the radio system components and, in particular, to match the impedance of the radio, the antenna and the feed line between the two components. A mismatch in impedance can result in a significant loss of radio signals.
To that end, a need exists for a system and method of providing an in-glass or concealed antenna that is capable of providing an impedance match with the remaining portion of the radio system.
The preferred embodiment of the present invention discloses an in-glass antenna system that includes adjustable impedance for impedance matching the in-glass antenna system with a radio receiver in a motor vehicle. The in-glass antenna system includes an in-glass slot antenna that is defined by an upper portion, a lower portion and two respective side portions. An in-glass impedance matching circuit is connected to the slot antenna, wherein the impedance matching circuit is capable of adjusting the impedance of the in-glass slot antenna.
The preferred in-glass impedance matching circuit comprises an in-glass conductive trace that is connected to a predetermined point on, preferentially, the antenna feed structure within the in-glass slot antenna. The in-glass conductive trace runs substantially parallel with the upper portion of the in-glass slot antenna. In the preferred embodiments of the in-glass antenna system, three elements of the in-glass conductive trace may be adjusted to adjust the impedance of the in-glass slot antenna. Controlling these three parameters allows a reliable impedance match between the in-glass antenna system and the radio receiver to be obtained.
The first element or parameter that can be adjusted is the spacing of the conductive trace from the opposite portion of the in-glass slot antenna to which the in-glass conductive trace is connected to the in-glass slot antenna. Second, the length of the in-glass conductive trace can also be adjusted to adjust the impedance of the in-glass slot antenna. Third, the width of the in-glass conductive trace can be adjusted to adjust the impedance of the in-glass slot antenna.
Yet another embodiment of the present invention discloses a method of impedance matching an in-glass antenna system for a window with a radio receiver. In this preferred method, an in-glass slot antenna is provided that includes an in-glass antenna conductive trace that runs substantially parallel with a horizontal plane of the window. An in-glass conductive trace is connected to the in-glass antenna conductive trace that runs substantially parallel with a horizontal plane of the window for a predetermined distance. A first end of the in-glass conductive trace is grounded to the lower portion of the in-glass slot antenna and a second end of the in-glass conductive trace is used as a signal transmission output line.
The impedance of in-glass slot antenna can be adjusted by adjusting the predetermined distance, the spacing of the in-glass conductive trace from an edge of the window and the width of the in-glass conductive trace.
The case where the conductive trace matching circuit is connected to the lower portion of the in glass antenna is subsequently described and illustrated, however, the scope of the invention is not solely limited to this case as mentioned above. Further objects and advantages of the present invention will be apparent from the following description, reference being made to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.